Communication has moved in the recent decades towards digital networks carrying voice, facsimile, data and video signals. With the vast amount of data being exchanged over communications networks, it is apparent that data compression is a useful feature in these networks to increase the operation efficiency by transmitting the signals in a compressed form, thereby using the available bandwidth to simultaneously transmit more information. The cost and time savings as well as the benefit of having a faster connection are not negligible and are highly desirable, resulting in a constant demand for better and improved lossless data compression algorithms.
Data compression is a technique wherein a signal, or computer data which requires a certain number of bits for its representation, is represented or encoded, using a fewer number of bits. The ratio between the number of bits required for representing the original signal to the number of bits required by the encoded signal is known as the compression ratio. The complimentary process in which the signal or computer data is expanded and reconstructed to form its original representation is called decompression, decoding or reconstruction.
Data compression is a technology which has matured during the recent decades and comprises two major types of compression: lossy and lossless. In a lossy compression type of system, portions of the data that are determined to be less necessary are discarded making exact reconstruction or decompression of the signal impossible. Lossy compression is employed for physical signals such as speech, audio, images and video in which exact reconstruction of the original signal is usually not required for perceptive acceptability. Since such signals as those immediately described above are generally destined for human perception, such as by the human auditory or visual senses, minor differences between the original and reconstructed signals may either be undetected by human senses or tolerable in their degraded state.
In contrast, lossless compression enables an exact reconstruction of the original signal to be performed upon decompression. In other words, lossless compression achieves a perfect recreation of the original signal without the degraded or compromised characteristics of lossy compression techniques. One of the penalties of employing lossless compression is that the compression ratio or the ability to compress a large number of data bits into a smaller number of data bits is greatly reduced. For certain types of data information, it is imperative that perfect reconstruction of lossless data compression be employed rather than the compromised reconstruction approach characteristic of lossy compression techniques. For example, computer data must be precisely reconstructed otherwise disastrous effects might occur.
In U.S. Pat. No. 6,289,130 a data compression scheme is described which provides an algorithm to determine when as well as how to efficiently switch between transparent and compressed modes to provide and facilitate an improved compression ratio. Additionally, a temporary buffer is provided for use by the encoder in determining which of either transparent or compressed mode provides a more efficient transfer of a portion of data. In making a determination to transition between transmit modes, the incurred overhead associated with such transitions is also taken into account.
U.S. Pat. No. 5,177,480 describes a method of processing data for transmission from a transmitter to a receiver both of which are switchable between a compression mode in which the data stream is encoded by using a data compression algorithm and a transparent mode in which the data stream is transmitted in its non-encoded form. The method described comprises reading an input data stream at the transmitter, encoding at least part of the input data stream with the data compression algorithm to form a compressed data stream, monitoring the efficiency of compression of the compressed data stream and controlling the switching of the mode of the transmitter so that the input data stream is transmitted efficiently. In the transparent mode both the receiver and the transmitter check independently the efficiency of compression and switch to the compression mode if the transparent mode is determined to be inefficient. In the compression mode the transmitter determines the efficiency of compression and transmits a control code to the receiver, switching both the receiver and transmitter to the transparent mode if the compression mode is determined to be inefficient.
U.S. Pat. No. 5,648,773 discloses synchronized transmitter and receiver of a data compression transmission system which is operative to switch, when a compression is no longer effective, from a first data compression mode of operation to a second mode of operation called release mode and according to which the data are transmitted or received directly without compression or decompression, for the transmission and reception, respectively, of a predetermined number of data.
U.S. Pat. No. 7,263,233 describes an encoder which is operative in a compressed or a transparent mode that switches from one mode to the other based upon a data compressibility test. The test comprises comparing an N-segment sliding average of the number of bits required by the encoder in compressed mode to represent a segment of a fixed number of characters to the number of bits required by the encoder in transparent mode to represent the segment.
As may be appreciated, the decisions on whether to apply compression onto the received signal that are taken in accordance with the prior art methods, are typically based upon a prior attempt to compress at least part of the received signal to be transmitted (test signal), and upon determining the compression effect on that test signal, to take a decision on whether to transmit the signal in a compressed form or not. Some of the drawbacks associated with these prior art methods are, the need to go through the various steps of compression for at least a part of the received signal in order to establish the compression effect, and consequently waste compression resources, particularly if the signal is eventually determined to be a non-compressible signal.
Furthermore, in modern compressors another problem arises from the fact that once the test signal, which is, as previously explained, at least a part of the original signal (or the whole original signal itself), is compressed but the final decision is that the signal should not be transmitted in its compressed form, there is no way for the compressing machine to resume its preceding state (i.e. the state prior to its operating upon the test signal). Thus, for such cases, further resources must be utilized for duplicating and storing the compressor state prior to applying the compression upon the test signal, to enable the transmission of the signal in the non-compressed form.
The present invention is therefore directed to overcome such problems, and to provide a method for determining whether a signal that should be forwarded along a transmission path, can be transmitted essentially in a compressed form.